Change to C99 and add weak references

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.11)
 
-set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD 99)
 
 project(
   refcount

README.md

@@ -1,7 +1,7 @@
 # RefCount
 
 RefCount is a reference counting (thus the name) and garbage collection library
-for C. It is currently WIP and unfinished.
+written in standard C99.
 
 ### Building
 
@@ -23,5 +23,5 @@ You can generate documentation with:
 doxygen
 ```
 
-For now, you can look in the `test/` directory for some examples of the various
+You can look in the `test/` directory for some examples of the various features
-features of RefCount in use.
+of RefCount in use.

include/refcount/allocator.h

@@ -22,19 +22,19 @@ extern "C" {
  */
 typedef struct RefcountAllocator {
     union {
-        void *(*malloc)(size_t size); //!< malloc implementation which takes no
+        void *(*no_data)(size_t size); //!< malloc implementation which takes no
                                        //!< data.
-        void *(*malloc_with_data)(
+        void *(*with_data)(size_t size,
-            size_t size,
+                           void *user_data); //!< malloc implementation that
-            void *user_data); //!< malloc implementation that takes a data
+                                             //!< takes a data argument.
-                              //!< argument.
+    } malloc;
-    };
     union {
-        void (*free)(void *ptr); //!< free implementation which takes no data.
+        void (*no_data)(
-        void (*free_with_data)(void *ptr,
+            void *ptr); //!< free implementation which takes no data.
+        void (*with_data)(void *ptr,
                           void *user_data); //!< free implementation that
                                             //!< takes a data argument.
-    };
+    } free;
     bool pass_data;
     void *user_data;
 } RefcountAllocator;
@@ -50,9 +50,9 @@ extern const RefcountAllocator *refcount_global_allocator;
 static inline void *refcount_malloc(const RefcountAllocator *alloc,
                                     size_t size) {
     if (alloc->pass_data) {
-        return alloc->malloc_with_data(size, alloc->user_data);
+        return alloc->malloc.with_data(size, alloc->user_data);
     }
-    return alloc->malloc(size);
+    return alloc->malloc.no_data(size);
 }
 
 /**
@@ -62,9 +62,9 @@ static inline void *refcount_malloc(const RefcountAllocator *alloc,
  */
 static inline void refcount_free(const RefcountAllocator *alloc, void *ptr) {
     if (alloc->pass_data) {
-        alloc->free_with_data(ptr, alloc->user_data);
+        alloc->free.with_data(ptr, alloc->user_data);
     } else {
-        alloc->free(ptr);
+        alloc->free.no_data(ptr);
     }
 }
 

include/refcount/refcount.h

@@ -103,16 +103,28 @@ void refcount_context_destroy(RefcountContext *ctx);
  */
 typedef struct RefcountEntry {
     bool is_static; //!< Whether the object is static.
+    RefcountList *weak_refs; //<! List of #RefcountWeakref structures for
+                             //<! holding thread safe weak references.
     union {
         struct {
             uint64_t ref_count; //!< The object's reference count.
             RefcountList *gc_root; //!< The object's GC root, or NULL.
-        };
+        } counted;
         RefcountList *static_entry; //!< The object's static list entry, never
-                                    //!< NULL for registed statics.
+                                    //!< NULL for registered statics.
-    };
+    } impl;
 } RefcountEntry;
 
+/**
+ * Structure holding the required information for a weak reference. That is, a
+ * reference that does not prevent an object from being de-allocated.
+ */
+typedef struct RefcountWeakref {
+    RefcountList *entry; //!< Link in the #RefcountEntry list of the object this
+                         //!< references that points to this reference.
+    void *data; //<! The object this weak ref references (not the entry).
+} RefcountWeakref;
+
 /**
  * Return a pointer to the entry associated with an object.
  * @param ctx The #RefcountContext
@@ -129,7 +141,8 @@ typedef struct RefcountEntry {
  * @param obj The object to test
  * @return Whether or not the object is static
  */
-static inline bool refcount_context_is_static(RefcountContext *ctx, void *obj) {
+static inline bool refcount_context_is_static(const RefcountContext *ctx,
+                                              void *obj) {
     return REFCOUNT_OBJECT_ENTRY(ctx, obj)->is_static;
 }
 
@@ -141,12 +154,12 @@ static inline bool refcount_context_is_static(RefcountContext *ctx, void *obj) {
  * @param obj The object
  * @return The number of references the object has
  */
-static inline size_t refcount_context_num_refs(RefcountContext *ctx,
+static inline size_t refcount_context_num_refs(const RefcountContext *ctx,
                                                void *obj) {
-    return REFCOUNT_OBJECT_ENTRY(ctx, obj)->ref_count;
+    return REFCOUNT_OBJECT_ENTRY(ctx, obj)->impl.counted.ref_count;
 }
 
-void refcount_context_init_obj(RefcountContext *ctx, void *obj);
+void refcount_context_init_obj(const RefcountContext *ctx, void *obj);
 
 bool refcount_context_init_static(RefcountContext *ctx, void *obj);
 
@@ -163,7 +176,7 @@ static inline void refcount_context_deinit_static_as_callback(void *obj,
     refcount_context_deinit_static(ctx, obj);
 }
 
-void *refcount_context_ref(RefcountContext *ctx, void *obj);
+void *refcount_context_ref(const RefcountContext *ctx, void *obj);
 
 void *refcount_context_unref(RefcountContext *ctx, void *obj);
 
@@ -180,6 +193,58 @@ void *refcount_context_float(RefcountContext *ctx, void *obj);
 
 ptrdiff_t refcount_context_garbage_collect(RefcountContext *ctx);
 
+RefcountWeakref *refcount_context_make_weakref(const RefcountContext *ctx,
+                                               void *obj);
+
+void refcount_context_destroy_weakref(const RefcountContext *ctx,
+                                      RefcountWeakref *wr);
+
+/**
+ * Return weather the object referenced by a weak reference still exists.
+ * @param ctx The #RefcountContext
+ * @param wr The weak reference
+ * @return Weather the reference is still valid
+ */
+static inline bool refcount_context_weakref_is_valid(const RefcountContext *ctx,
+                                                     RefcountWeakref *wr) {
+    return wr->data;
+}
+
+void *refcount_context_ref_weakref(const RefcountContext *ctx,
+                                   const RefcountWeakref *wr);
+
+/**
+ * Convenience function that calls #refcount_context_ref_weakref followed by
+ * #refcount_context_destroy_weakref.
+ * @param ctx The #RefcountContext
+ * @param wr The weak reference
+ * @return The newly referenced object, or NULL if the object no longer exists
+ */
+static inline void *refcount_context_strengthen(const RefcountContext *ctx,
+                                                RefcountWeakref *wr) {
+    void *obj = refcount_context_ref_weakref(ctx, wr);
+    refcount_context_destroy_weakref(ctx, wr);
+    return obj;
+}
+
+/**
+ * Create a weak reference for an object and then unref it. This is the same as
+ * calling #refcount_context_make_weakref followed by #refcount_context_unref.
+ * @param ctx The #RefcountContext
+ * @param obj The object to create a weak reference for then unref
+ * @return The newly created weak reference, or NULL if an allocation error
+ * occurred. In this case the object is not unrefed.
+ */
+static inline RefcountWeakref *refcount_context_weaken(RefcountContext *ctx,
+                                                       void *obj) {
+    RefcountWeakref *wr = refcount_context_make_weakref(ctx, obj);
+    if (!wr) {
+        return NULL;
+    }
+    refcount_context_unref(ctx, obj);
+    return wr;
+}
+
 /**
  * Same as #refcount_context_is_static, but only operates on the global
  * context.
@@ -273,6 +338,63 @@ static inline ptrdiff_t refcount_garbage_collect(void) {
     return refcount_context_garbage_collect(refcount_default_context);
 }
 
+/**
+ * Same as #refcount_context_make_weakref, but operates on the global context.
+ * @param obj The object to reference
+ * @return The new weak reference, or NULL if an allocation error occurred
+ */
+static inline RefcountWeakref *refcount_make_weakref(void *obj) {
+    return refcount_context_make_weakref(refcount_default_context, obj);
+}
+
+/**
+ * Same as #refcount_context_destroy_weakref, but operates on the global
+ * context.
+ * @param wr The weak reference
+ */
+static inline void refcount_destroy_weakref(RefcountWeakref *wr) {
+    refcount_context_destroy_weakref(refcount_default_context, wr);
+}
+
+/**
+ * Same as #refcount_context_ref_weakref, but operates on the global context.
+ * @param wr The weak reference
+ * @return The newly referenced object, or NULL if the object no longer exists
+ */
+static inline void *refcount_ref_weakref(RefcountWeakref *wr) {
+    return refcount_context_ref_weakref(refcount_default_context, wr);
+}
+
+/**
+ * Same as #refcount_context_weakref_is_valid, but operates on the global
+ * context.
+ * @param wr The weak reference
+ * @return Weather the reference is still valid
+ */
+static inline bool refcount_weakref_is_valid(RefcountWeakref *wr) {
+    return refcount_context_weakref_is_valid(refcount_default_context, wr);
+}
+
+/**
+ * Same as #refcount_context_strengthen, but operates on the global context.
+ * @param wr The weak reference
+ * @return The newly referenced object, or NULL if the object no longer
+ * exists
+ */
+static inline void *refcount_strengthen(RefcountWeakref *wr) {
+    return refcount_context_strengthen(refcount_default_context, wr);
+}
+
+/**
+ * Same as #refcount_context_weaken, but operates ojn the global context.
+ * @param obj The object to create a weak reference for then unref
+ * @return The newly created weak reference, or NULL if an allocation error
+ * occurred. In this case the object is not unrefed.
+ */
+static inline RefcountWeakref *refcount_weaken(void *obj) {
+    return refcount_context_weaken(refcount_default_context, obj);
+}
+
 #ifdef __cplusplus
 }
 #endif

src/allocator.c

@@ -10,8 +10,8 @@
  * Initial value of #refcount_global_allocator.
  */
 static const RefcountAllocator DEFAULT_ALLOCATOR = {
-    .malloc = malloc,
+    .malloc.no_data = malloc,
-    .free = free,
+    .free.no_data = free,
     .pass_data = false,
     .user_data = NULL,
 };

src/refcount.c

@@ -94,11 +94,12 @@ void refcount_context_destroy(RefcountContext *ctx) {
  * @param ctx The #RefcountContext
  * @param obj The object to initialize
  */
-void refcount_context_init_obj(RefcountContext *ctx, void *obj) {
+void refcount_context_init_obj(const RefcountContext *ctx, void *obj) {
     if (obj) {
         ENTRY->is_static = false;
-        ENTRY->gc_root = NULL;
+        ENTRY->impl.counted.gc_root = NULL;
-        ENTRY->ref_count = 0;
+        ENTRY->impl.counted.ref_count = 0;
+        ENTRY->weak_refs = NULL;
     }
 }
 
@@ -115,7 +116,8 @@ bool refcount_context_init_static(RefcountContext *ctx, void *obj) {
     if (!ctx->static_objects) {
         return false;
     }
-    ENTRY->static_entry = ctx->static_objects;
+    ENTRY->impl.static_entry = ctx->static_objects;
+    ENTRY->weak_refs = NULL;
     return true;
 }
 
@@ -134,6 +136,27 @@ static inline bool obj_held_refs(RefcountContext *ctx, void *obj,
     return true;
 }
 
+/**
+ * Call back used from #clear_weak_references.
+ * @param wr_raw The #RefcountWeakref object
+ */
+static void clear_weak_reference_callback(void *wr_raw) {
+    RefcountWeakref *wr = wr_raw;
+    wr->entry = NULL;
+    wr->data = NULL;
+}
+
+/**
+ * Clear all weak references of an object without freeing them.
+ * @param ctx The #RefcountContext
+ * @param obj The object to clear
+ */
+static inline void clear_weak_references(const RefcountContext *ctx,
+                                         void *obj) {
+    refcount_list_free_full(ENTRY->weak_refs, clear_weak_reference_callback,
+                            &ctx->alloc);
+}
+
 /**
  * Unregister a static object in a context.
  * @param ctx The #RefcountContext
@@ -146,8 +169,9 @@ bool refcount_context_deinit_static(RefcountContext *ctx, void *obj) {
         if (!obj_held_refs(ctx, obj, &held_refs)) {
             return false;
         }
+        clear_weak_references(ctx, obj);
         ctx->static_objects = refcount_list_remove_full(
-            ctx->static_objects, ENTRY->static_entry, NULL, &ctx->alloc);
+            ctx->static_objects, ENTRY->impl.static_entry, NULL, &ctx->alloc);
         refcount_list_free_with_data_full(
             held_refs, refcount_context_unref_as_callback, ctx, &ctx->alloc);
         return true;
@@ -163,11 +187,11 @@ bool refcount_context_deinit_static(RefcountContext *ctx, void *obj) {
  * @param obj The object to reference
  * @return The input object
  */
-void *refcount_context_ref(RefcountContext *ctx, void *obj) {
+void *refcount_context_ref(const RefcountContext *ctx, void *obj) {
     if (!obj) {
         return NULL;
     } else if (!ENTRY->is_static) {
-        ++ENTRY->ref_count;
+        ++ENTRY->impl.counted.ref_count;
     }
     return obj;
 }
@@ -180,13 +204,13 @@ void *refcount_context_ref(RefcountContext *ctx, void *obj) {
  * @return True on success
  */
 static bool track_gc_root(RefcountContext *ctx, void *obj) {
-    if (!ENTRY->gc_root) {
+    if (!ENTRY->impl.counted.gc_root) {
         ctx->gc_roots =
             refcount_list_push_full(ctx->gc_roots, obj, &ctx->alloc);
         if (!ctx->gc_roots) {
             return false;
         }
-        ENTRY->gc_root = ctx->gc_roots;
+        ENTRY->impl.counted.gc_root = ctx->gc_roots;
     }
     return true;
 }
@@ -198,9 +222,9 @@ static bool track_gc_root(RefcountContext *ctx, void *obj) {
  * @param obj The object to untrack
  */
 static void remove_gc_root(RefcountContext *ctx, void *obj) {
-    ctx->gc_roots = refcount_list_remove_full(ctx->gc_roots, ENTRY->gc_root,
+    ctx->gc_roots = refcount_list_remove_full(
-                                              NULL, &ctx->alloc);
+        ctx->gc_roots, ENTRY->impl.counted.gc_root, NULL, &ctx->alloc);
-    ENTRY->gc_root = NULL;
+    ENTRY->impl.counted.gc_root = NULL;
 }
 
 /**
@@ -222,11 +246,11 @@ static void *unref_to_queue(RefcountContext *ctx, void *obj,
         return obj;
     } else if (obj == toplevel) {
         return NULL;
-    } else if (ENTRY->ref_count <= 1) {
+    } else if (ENTRY->impl.counted.ref_count <= 1) {
         *queue = refcount_list_push_full(*queue, obj, &ctx->alloc);
         return NULL;
     }
-    --ENTRY->ref_count;
+    --ENTRY->impl.counted.ref_count;
     track_gc_root(ctx, obj);
     return obj;
 }
@@ -258,6 +282,7 @@ static void unref_to_queue_as_callback(void *obj, void *ctx_and_queue_raw) {
  * @param obj The object to destroy
  */
 static inline void destroy_object(RefcountContext *ctx, void *obj) {
+    clear_weak_references(ctx, obj);
     remove_gc_root(ctx, obj);
     if (ctx->destroy_callback) {
         ctx->destroy_callback(obj, ctx->user_data);
@@ -326,11 +351,11 @@ void *refcount_context_float(RefcountContext *ctx, void *obj) {
         return NULL;
     } else if (ENTRY->is_static) {
         return obj;
-    } else if (!ENTRY->ref_count) {
+    } else if (!ENTRY->impl.counted.ref_count) {
         BREAKPOINT(FLOAT, ctx, obj);
         return obj;
     }
-    if (--ENTRY->ref_count) {
+    if (--ENTRY->impl.counted.ref_count) {
         track_gc_root(ctx, obj);
     } else {
         remove_gc_root(ctx, obj);
@@ -371,7 +396,8 @@ static bool free_roots_foreach(void *obj, void *ignored, void *user_data) {
     }
     struct ContextAndRootPtr *data = user_data;
     if (*data->root_ptr
-        && *data->root_ptr == REFCOUNT_OBJECT_ENTRY(data->ctx, obj)->gc_root) {
+        && *data->root_ptr
+               == REFCOUNT_OBJECT_ENTRY(data->ctx, obj)->impl.counted.gc_root) {
         *data->root_ptr = (*data->root_ptr)->next;
         data->did_update = true;
     }
@@ -413,7 +439,7 @@ static ptrdiff_t check_gc_root(RefcountContext *ctx, RefcountList **root_ptr) {
         if (ht_has(counts, obj)) {
             count = HT_UUNSTUFF(ht_get(counts, obj));
         } else {
-            count = REFCOUNT_OBJECT_ENTRY(ctx, obj)->ref_count;
+            count = REFCOUNT_OBJECT_ENTRY(ctx, obj)->impl.counted.ref_count;
             ++seen_objects;
         }
         queue = refcount_list_pop_full(queue, NULL, &ctx->alloc);
@@ -460,3 +486,63 @@ ptrdiff_t refcount_context_garbage_collect(RefcountContext *ctx) {
     }
     return total_cleared;
 }
+
+/**
+ * Create a new weak reference for an object. A weak reference will allow safe
+ * access to the referenced object without holding a reference. That is, the
+ * referenced object can be accessed until it's reference count falls to 0 and
+ * it is freed. After this, attempts to use the weak reference will just return
+ * NULL to indicate that the referenced object is no longer in existence.
+ * @param ctx The #RefcountContext
+ * @param obj The object for which to create a weak reference
+ * @return The newly created weak reference, or NULL if an allocated error
+ * occurred.
+ */
+RefcountWeakref *refcount_context_make_weakref(const RefcountContext *ctx,
+                                               void *obj) {
+    RefcountWeakref *wr = refcount_malloc(&ctx->alloc, sizeof(RefcountWeakref));
+    if (!wr) {
+        return NULL;
+    }
+    RefcountList *new_weak_refs =
+        refcount_list_push_full(ENTRY->weak_refs, wr, &ctx->alloc);
+    if (!new_weak_refs) {
+        refcount_free(&ctx->alloc, wr);
+        return NULL;
+    }
+    ENTRY->weak_refs = new_weak_refs;
+    wr->entry = new_weak_refs;
+    wr->data = obj;
+    return wr;
+}
+
+/**
+ * Destroy a weak reference. This has no effect on the reference count of the
+ * original object.
+ * @param ctx The #RefcountContext
+ * @param wr The weak reference
+ */
+void refcount_context_destroy_weakref(const RefcountContext *ctx,
+                                      RefcountWeakref *wr) {
+    if (wr->data) {
+        void *obj = wr->data;
+        ENTRY->weak_refs = refcount_list_remove_full(
+            ENTRY->weak_refs, wr->entry, NULL, &ctx->alloc);
+    }
+    refcount_free(&ctx->alloc, wr);
+}
+
+/**
+ * Add a reference to an object referenced by a weak reference and return the
+ * object. If the referenced object no longer exists, return NULL.
+ * @param ctx The #RefcountContext
+ * @param wr The weak reference
+ * @return The newly referenced object, or NULL
+ */
+void *refcount_context_ref_weakref(const RefcountContext *ctx,
+                                   const RefcountWeakref *wr) {
+    if (!wr->data) {
+        return NULL;
+    }
+    return refcount_context_ref(ctx, wr->data);
+}

test/alloc.h

@@ -8,7 +8,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#if __has_attribute(unused)
+#if defined(__has_attribute) && __has_attribute(unused)
 #    define UNUSED __attribute__((unused))
 #else
 #    define UNUSED
@@ -67,8 +67,8 @@ static UNUSED char *counting_strdup(const char *str) {
 }
 
 static UNUSED const RefcountAllocator COUNTING_ALLOCATOR = {
-    .malloc = counting_malloc,
+    .malloc.no_data = counting_malloc,
-    .free = counting_free,
+    .free.no_data = counting_free,
 };
 
 #endif

test/test_refcount.c

@@ -113,6 +113,42 @@ int main(int argc, const char **argv) {
 
     assert(refcount_context_garbage_collect(c) == 26);
 
+    a = make_a(c, 0, "a");
+
+    RefcountWeakref *w = refcount_context_make_weakref(c, a);
+    assert(w);
+    assert(refcount_context_num_refs(c, a) == 0);
+
+    b = refcount_context_strengthen(c, w);
+    assert(b);
+    assert(a == b);
+    assert(refcount_context_num_refs(c, a) == 1);
+
+    refcount_context_ref(c, a);
+    assert(refcount_context_num_refs(c, a) == 2);
+
+    RefcountWeakref *x = refcount_context_weaken(c, a);
+    w = refcount_context_make_weakref(c, a);
+    assert(refcount_context_num_refs(c, a) == 1);
+    assert(w != x);
+    refcount_context_destroy_weakref(c, x);
+
+    refcount_context_ref(c, a);
+    assert(refcount_context_num_refs(c, a) == 2);
+
+    x = refcount_context_weaken(c, a);
+    assert(refcount_context_num_refs(c, a) == 1);
+    assert(w != x);
+    assert(refcount_context_weakref_is_valid(c, w));
+    assert(refcount_context_weakref_is_valid(c, x));
+
+    assert(!refcount_context_unref(c, a));
+    assert(!refcount_context_weakref_is_valid(c, w));
+    assert(!refcount_context_weakref_is_valid(c, x));
+
+    refcount_context_destroy_weakref(c, w);
+    refcount_context_destroy_weakref(c, x);
+
     refcount_context_destroy(c);
 
     check_allocator_status();